A former Royal Marine charged with spying for Hong Kong warned a custody sergeant that he would harm himself once he was free, days before he was granted bail and found dead in a park, a jury inquest has heard.

Matthew Trickett, 37, a Home Office immigration officer who also worked as a private investigator, was found dead in Grenfell Park in Maidenhead on 19 May 2024. His death came a week after he was charged with two offences under the National Security Act 2023. The jury inquest into his death is being held at Reading coroner’s court.

Arrest and warnings in custody

On Tuesday, the inquest heard that Trickett was arrested in Yorkshire on 1 May 2024 and tried to harm himself on 11 May while being held in police custody in London. After staff intervened, he told officers that he would not harm himself while in their care but would do so at some point once he was free.

Police Sergeant Del May, of the Metropolitan Police, told the coroner’s court that when Trickett arrived at the police station in London he was assigned the minimum level of monitoring, with observation every 60 minutes, because he did not present any major medical or mental health issues.

The court heard that officers attended Trickett’s cell and stopped him harming himself after he was spotted acting differently. “He apologised and actually said to me that he wasn’t going to do anything else to harm himself while he was in the custody suite. He said he had a lot of respect for the police and felt he was treated well,” Sergeant May said. “He said he would harm himself but not at the police station — he didn’t want any of us to get in trouble. He said he would do it at some point, but not whilst he was in custody.”

Sergeant May told the court that Trickett was then put under heightened supervision, with a check at least every 30 minutes. Asked whether there was a reasonable expectation that Trickett would be remanded, he said: “I would have thought so, yes.” Asked why, he said: “Because he said clearly that he was going to harm himself unless he was in the police station.”

The charges and bail

On 12 May, Trickett was charged with assisting a foreign intelligence service, by agreeing to undertake information gathering, surveillance and acts of deception likely to materially assist a foreign intelligence service, and with foreign interference. The foreign intelligence service was identified in court as that of Hong Kong.

After appearing in court on 13 May, Trickett was bailed with a condition to remain at home during certain hours. Serco was tasked with fitting his electronic tag but later reported to Thames Valley Police that it had not been able to monitor him. The force attempted to arrest Trickett but could not find him. He was later found dead in a park in Maidenhead, where he lived.

Trickett had served in the Royal Marines, including in the Arctic Circle, Afghanistan and Brunei. He was charged alongside two other men, who were accused of monitoring, surveillance and harassment of pro-democracy activists in the UK.

Co-defendants jailed

Earlier this year, Trickett’s co-defendants, Peter Wai, 41, a Border Force official, and Bill Yuen, 66, a Hong Kong trade official, were jailed for ten years and eight years respectively after being found guilty of running a shadow policing operation targeting dissidents.

The inquest continues, and no conclusion has yet been reached. Anyone affected by the issues in this story can contact Samaritans free of charge on 116 123. Read the inquest report in The Times, with background from the BBC.